Hi when I read Noodles first suggestion I thought she meant one thing but then seemed to mean something else - so not sure if this is a new suggestion or just a re-wording of already-suggested...
Anyway. I don't know much about Tourette's. So don't know if this is possible. Myself with allergies I sneeze, often loudly violently unexpectedly. Yet over the years I've trained myself to have a few Very short moments to reach for a tissue, if I'm keeping them handy, mute phone when working, or to exit a room (like in church). NOT THE SAME, I KNOW!
Well by now my birdies know my "signs" of an on-coming sneeze so I don't try to give them any other verbal warning. BUT with other things, I do.
Before crumpling a bottle or bag, or making other sudden noise, i will say "Loud Noise."
IF a noise occurs Unexpectedly & I was not able to warn them, i will Apologize, and say, "oh, I'm sorrrryyy, I'm sooo soorrryy for the Loud Noise, ooohhh," ETC.
Idea being - I use the words "Loud Noise" as an Alert to them, that something UNexpected and startling Might be about to occur. And/or as a calming-cue afterwards to let them know everything is still "safe" despite them having been startled.
Is there something you can do like that - if you feel a tic / tics about to occur - some statement or sound you can always say, or motion you can always make - before it's gonna start? IF so, the budgies will learn it's a warning sign for something possibly unexpected / possible scary.
Also then, IF you don't manage to warn them first, you can use that word / phrase / motion afterward while you apologize to them soothingly and explain that "...it's alllllrrighht, it's oookkaaay..."
Also, even if giving them a warning-cue does Not work for you, making a habit of always giving a soothing apology afterwards, especially if you can add certain cue words to that, will help them recover more quickly. For example, if you always say "oh, it's okay, it was only tourette, it's okay" ...or, whatever words work for you!... but, in a Calming Soothing voice, after a while they will learn to at least calm down quickly afterwards.
The after-soothing is probably fairly important. My Jefferson-budgie panics quite easily, but he is willing to be soothed when I gently tell him "it's oookkaay." Without that, he will stay in a state of panic for a long time. So even if your specific tics change, or are long-lasting, it is important to reassure the birds afterwards. Over time, this can help them to understand to be less alarmed even with new variations.